1. Field of the Invention
The present invention relates to a white light emitting diode (LED) and a method of manufacturing the same.
2. Description of the Related Art
An LED is referred to as a device which generates minority carriers (electrons or holes) injected by using the p-n junction structure of semiconductor and emits light by recombining the minority carriers. As for the LED, a red LED using GaAsP or the like, a green LED using GaP or the like, and a blue LED using InGaN/AlGaN double hetero structure are provided.
The LED has low power consumption and a long lifespan. Further, the LED can be installed in a narrow space, and has high resistance to vibration. The LED is used as a display device and a backlight unit. Recently, researches are being actively conducted to apply the LED as a general lighting.
Recently, white LEDs as well as red, blue, or green LEDs are launched on the market.
Since the white LEDs can be applied to various fields, it is expected that demand for the white LEDs is rapidly increasing.
A technique for implementing white light in the LED can be roughly divided into two techniques.
In the first technique, red, green, and blue LED chips are installed adjacent to each other, and lights emitted from the respective LED chips are mixed to implement white light. However, since the respective LED chips have different thermal or time characteristics, the color tones of the LED chips are changed depending on the surrounding environment. In particular, color spots may occur, which makes it difficult to implement a uniform mixed color.
In the second technique, phosphor is disposed in an LED chip. Some of primarily-emitted light from the LED chip and secondarily-emitted light, of which the wavelength is converted by the phosphor, are mixed to implement white light. That is, phosphor which is excited by ultraviolet (UV) light so as to emit visible light from blue to red is coated on the LED chip which emits UV light, thereby obtaining white light. Alternately, on an LED chip which emits blue light, phosphor is distributed, the phosphor emitting yellow-green or yellow light by using the blue light as an excitation source. Then, white light can be obtained by the blue light emitted from the LED chip and the yellow-green or yellow light emitted from the phosphor.
Between them, the second technique is generally used. In particular, the technique for implementing white light by using the blue LED chip and the yellow-green or yellow phosphor is most frequently used.
FIG. 1 is a cross-sectional view of a conventional lamp-type white LED which uses a white LED chip and yellow light emitting phosphor so as to implement white light.
As shown in FIG. 1, the lamp-type white LED 10 includes a mount lead 11, an inner lead 12, and an LED chip 14 installed in a reflector cup 20 formed in the upper portion of the mount lead 11. Further, n- and p-electrodes of the LED chip 14 are electrically connected to the mount lead 11 and the inner lead 12, respectively, through a wire 15.
The LED chip 14 is covered by a phosphor layer 150 which is obtained by mixing phosphor materials with transparent resin. The above-described components are surrounded by an encapsulation member 17.
The reflector cup 20 is coated with silver (Ag) and aluminum (Al) to reliably reflect visible light.
FIGS. 2A and 2B are diagrams simply showing a case where phosphor materials are disposed in the reflector cup.
As shown in the drawings, the LED chip 14 is mounted on the bottom surface of the reflector cup 20, and the transparent resin 16 is filled in the reflector cup 20. Further, the phosphor materials 19 are distributed in the transparent resin 16.
As shown in FIG. 2A, the phosphor materials 19 may be uniformly distributed in the transparent resin 16. Alternately, as shown in FIG. 2B, the phosphor materials 19 may be concentrated on the surface of the LED chip 14.
When a current is applied, the LED 10 including the phosphor materials 19 mixed with the transparent resin 16 implements white light by combining blue light emitted from the LED chip 14 and yellow light emitted from the phosphor materials 16 using some of the blue light as an excitation source.
However, some of light emitted from the phosphor materials 19, which are excited by the light emitted from the LED chip 14, collides with the surface of the LED chip 14 so as to be re-absorbed. Therefore, light emission efficiency decreases.
As shown in FIG. 2B, when the phosphor materials 19 are concentrated on the surface of the LED chip 14, it is highly likely that the light emitted from the phosphor materials 19 collides with the surface of the LED chip 14, compared with the case where the phosphor materials 19 are uniformly distributed in the transparent resin 16. Therefore, the light emission characteristic is degraded.